This story has popped up on the net everywhere recently.
From what I can tell it is based on a poorly done and/or out of date view of motorcycles.
From what I understand the testing lumps together:
Road Legal motorcycles, 2-stroke scooters, non-road legal 2-stroke dirt bikes, non road legal ATVs. And it assume they all emit the same pollutants.
So basically they are using the average polutants for a wide range of vehicles (Many of which were never designed to pass any emissions testing what so ever) and using it to describe on-road motorcycles.
They mention that most motorcycles do not have catalytic converters, but any bike that meets the 2004 Euro standard (so is for sale in Europe now) has a catalytic converter. The newest standard (Euro tier 3) is pretty strict. Read any review of an internationally released bike and they’ll mention how it meets those standards. The California standards are slightly more strict. So any bike that passes the California EPA testing is a clean machine.
Here is a slightly more in-depth look at motorcycle EPA standards (circa 2007).
A US Tier 1 (2006) Motorcycle (so any motorcycle sold since 2006) is required to emit no more than:
1.4g/kg Hydrocarbons + NOx Combined
Teir 2 (2008 in California, 2010 rest of USA)
Reduces Hydrocrabons and NOx to 0.8g/kg
Now, if we compare we can see that a current light-duty vehicle(passenger car, more strick that trucks and SUVs) is required to emit less than: (from: http://www.epa.gov/otaq/cert/veh-cert/b00001.pdf )
and 3.4g/kg Carbonmonoxide
Okay, so yes, cars definitely produce less polutants. But 10x? No.
By law a car produces 0.65 grams of hydrocarbons and NOx per kilogram as compared to the motorcycle’s 1.4g/kg (a motorcycle produces just over twice the hydrocarbons and NOx per kilogram).
And a car 3.4 grams of carbonmonoxide as compard to the bike’s 12g/kg. Which means the bike produces 3.5x the amount of carbonmonoxide as a car.
Now, what I’m not entirely sure on is the measure of g/kg. Is it one kilogram of fuel or one kilogram of exhaust gases (most likely the later). In either case this means things are better for the bikes than it looks. Because a bike uses less petrol (and thus makes a smaller amount of exhaust).
The article sights motorcycles have roughly twice the fuel efficency as cars. And given that 50mpg seems to be a fairly often sighted number for motorcycle economy, and 25mpg for cars, we’ll play fast and loose and say that a motorcycle produces one half the amount of exhaust as a car for the same distance travelled.
Following this generalization the motorcycles make roughly equivilant hydrocarbons and NOx to passenger cars and produce twice the carbonmonoxide per distance travelled.
So once again, are motorcycles more polluting than cars? Yes. They produce roughly twice the carbonmonoxide that a car does. They produce roughly the same hydrocarbons. Is a Hummer less polluting? NO because it produces far more exhaust per distance travelled than any motorcycle does.